Field of the Invention
The present invention relates to a drive control technique for a front- and rear-wheel drive vehicle which gives a sufficient driving force while improving turning performance of the vehicle and enables smooth driving.
Description of the Related Art
Patent Document 1 (Japanese Patent Laid-Open No. H05-16872) describes a front- and rear-wheel drive two-wheeler in which a drive source of a rear wheel and a motor driving source of a front wheel are drive-controlled individually and a motor is mounted on a steering system. With this front- and rear-wheel drive two-wheeler, influence of a front wheel on steering is lessened by mounting the motor on the steering system.
However, with the front- and rear-wheel drive two-wheeler according to Patent Document 1, when a vehicle body tilts (hereinafter “banks”) to either right or left during turning of the vehicle, a tire-to-ground contact point moves inward of a steering axis center in a turning direction, and consequently when a driver opens an accelerator (accelerate the vehicle), increases in driving force of the motor may sometimes affect aligning torque of the steering system.
With a normal rear-wheel drive vehicle, the tire-to-ground contact point moves inward of the steering axis center in the turning direction during turning of the vehicle, and consequently moment is generated around a center of a rotation axis for steering by running resistance acting on a tire tread and the moment acts to steer the vehicle inward (in the turning direction). In this case, even when the driver gradually opens the accelerator from OFF, a direction of force applied to a front wheel does not change.
With a front- and rear-wheel drive two-wheeler such as described in Patent Document 1, when the driver opens the accelerator to give driving force to the front wheel and the driving force overcomes the running resistance, the moment around the center of the rotation axis for steering acts in an opposite direction, acting to steer the vehicle outward (in a direction opposite the turning direction). Consequently, a direction and magnitude of a steering force required for handling changes, which may give the driver a sense of discomfort.